The invention relates to a turbine for an exhaust gas turbocharger of an internal combustion engine.
A turbine of this kind for an exhaust gas turbocharger of an internal combustion engine is already known, for example, from DE 10 2008 039 085 A1.
The turbine comprises a turbine housing, which has a receiving region. The turbine further comprises a turbine wheel which is at least partly, in particular at least predominately or completely, arranged in the receiving region and is rotatable relative to the turbine housing about an axis of rotation.
The turbine also has at least one channel which is formed by the turbine housing and by means of which the exhaust gas flowing through the channel can be or—during an operation of the turbine—is guided into the receiving region and to the turbine wheel. The exhaust gas flowing through the channel can flow out of and into the receiving region such that the exhaust gas flowing into the receiving gas can flow against and thus drive the turbine wheel.
The turbine further comprises a tongue slide which has at least one tongue that is associated with the channel and can slide relative to the turbine housing about the axis of rotation. A flow cross section of the channel associated with the tongue can be adjusted by means of the tongue. The exhaust gas flowing through the channel can be conveyed into the receiving region via the flow cross section and supplied to the turbine wheel. In other words, the channel leads into the receiving region via the associated flow cross section such that the exhaust gas flowing out of the channel and into the receiving channel flows out of the channel outlet region and into the receiving region via the flow cross section.
In addition, DE 10 2012 016 984 A1 also discloses a turbine for an exhaust gas turbocharger of an internal combustion engine having a tongue slide of this kind. Furthermore, DE 199 18 232 A1 discloses a multi-cylinder internal combustion engine.
The object of the present invention is that of further developing a turbine of the kind mentioned at the outset such that a particularly efficient operation can be realized.
In order to further develop a turbine such that a particularly efficient operation, and thus an operation that has a favorable degree of effectiveness, can be achieved, according to the invention the turbine is a half-axial turbine in which a flow direction, in which the exhaust gas flows from the channel through the flow cross section into the receiving region and thus to the turbine wheel during an operation of the turbine, extends obliquely to the axial direction and obliquely to the radial direction of the turbine wheel. In particular, the flow direction extends obliquely to the radial direction and obliquely to the axial direction of the turbine wheel for example in a plane spanned by the axial direction and by the radial direction of the turbine wheel, such that the exhaust gas is not supplied to the turbine wheel, in particular blades of a turbine wheel, for instance strictly in the radial direction or strictly in the axial direction, but rather the exhaust gas from the channel is supplied to the turbine wheel half-axially, i.e., obliquely to the axial direction and obliquely to the radial direction.
The invention is based in particular on the following knowledge: the continuing tightening of emission thresholds, in particular with respect to NOx and soot emissions, has had a significant influence on charging systems. Such a charging system is used in an internal combustion engine, the charging system being used to supply the internal combustion engine, in particular at least one combustion chamber, designed for example as a cylinder, of the internal combustion engine, with compressed air. Such a charging system therefore comprises at least one exhaust gas turbocharger which has a turbine that can be driven by exhaust gas from the internal combustion engine, and a compressor for compressing the air to be supplied to the internal combustion engine. The compressor can be driven by the turbine. Since the turbine can be driven by exhaust gas, the energy contained in the exhaust gas can be used to compress the air. Owing to increasing requirements with respect to the provision of charging pressure as a result of high specific power requirements and high EGR rates (EGR—exhaust gas recirculation) above the medium load range through to full loading, it is cogent to geometrically scale down the turbines of the charging systems further and further. The required turbine powers are thus also realized by increasing the build-up ability or by reducing the absorption capacity of the turbines in conjunction with the particular internal combustion engine.
Furthermore, particle or soot filters are commonly used, by means of which particles, in particular soot particles, can be filtered out of the particular exhaust gas of the internal combustion engine. The inlet pressure level of the turbines is therefore driven further upwards by the counter-pressure of the soot filter, as a result of which the turbines again have to be designed to have smaller dimensions and thus lower degrees of effectiveness in order to be able to satisfy power requirements on the compressor side for the air-exhaust gas supply. In this case, dual-flow, asymmetric turbines are used for example as core components of exhaust gas recirculation systems. A larger problem with respect to the EGR capability in connection with the required combustion air to be supplied of the internal combustion engine consists in particular in the low to medium engine operating range in the case of a high load. In the conventional design boundary conditions, which are also defined from the nominal point of the internal combustion engine from the charge exchange side or consumption side, the lower engine speed range cannot be optimally operated in an asymmetric, dual-flow, fixed geometry turbine. A fixed geometry turbine is understood to mean a turbine having a fixed turbine geometry, i.e., without a variable turbine geometry.
In order to be able to optimally adjust the relationship between the AGR rates and the required air-fuel ratios in a larger operating range, a dual-flow type of turbine of which the pulse-charging capacity in a cylinder group is more pronounced would be useful. Turbines which are specifically designed for pulse-charging have noticeably larger flow cross sections in order to exploit the larger energy fluctuations or pressure pulses that can be used. These high pressure pules of the internal combustion engine exist on the turbine of the exhaust gas turbocharger when the throttling and friction losses that usually occur at outlet valves of the internal combustion engine and in the manifold region are noticeably reduced going into the turbine by a corresponding geometric design. The reduction in the throttling and friction losses upstream of the turbines assists the achievement of the aim of the desired extreme pulse-charging, as a result of which an increase in the average overall degree of effectiveness of the exhaust gas energy exploitation can be achieved in spite of a large temporal fluctuation in the degree of effectiveness of the turbine.
The key to realizing weighting of the pulse-charging is provided by the segment turbine, which preferably ought to be provided with a variability of essential flow cross sections in order to also be able to persist in the upper engine speed range. In order to also advantageously realize future development trends, which are characterized by the further use of the present potential of improved exhaust gas after-treatment, in many cases the reduction in the degree of asymmetry of the turbines toward asymmetric turbine behavior is not implausible in order to be able to further influence consumption facilitation of internal combustion engines.
In developments of variable turbines, the simple radial turbine has been the focus for the turbocharger application for many decades, since the radial annular nozzle offers very favorable conditions for a relatively simple design of inlet variabilities compared with the complex variabilities of axial turbines. A simple radial turbine is understood to mean that exhaust gas is supplied to the turbine wheel strictly in the radial direction, in particular based on a plane spanned by the axial direction and the radial direction of the turbine wheel. Recently, there has been an increase in half-axial turbines which, however, are usually fitted without an inlet variability upstream of the turbine wheel. Since the deflection in the spatial flow in the wheel channels of half-axial turbines is significantly reduced, there is clear potential with respect to the degree of effectiveness of the half-axial turbines, which provides additional development incentives compared with the extensively developed radial turbines.
According to the invention, a half-axial turbine is combined with the tongue slide, which is designed or functions as a variability, the tongue slide being arranged at least in part upstream of the turbine wheel. The tongue slide is a variability which is arranged at least in part upstream of the turbine wheel since, by means of the tongue slide, the flow cross section, which is arranged upstream of the turbine wheel with respect to the flow direction of the exhaust gas through the turbine, of the channel, which is designed for example as a segment, can be adjusted, that is to say varied or altered. In order to vary or alter the flow cross section, the tongue is rotated or slid relative to the turbine axis about the axis of rotation. As a result, the turbine can be advantageously adapted to different operating points of the internal combustion engine such that a particularly advantageous operation, and in particular an operation that has a favorable degree of effectiveness and is efficient, can be shown.
The turbine according to the invention therefore constitutes a further development of a tongue-slide turbine, which can increase the series relevance in particular in respect of MDEG engines. The tongue slide is a thermally robust option, which is favorable in terms of installation space and cost, for varying the channel flow cross section arranged upstream of the turbine wheel. The channel extends for example in the circumferential direction of the turbine wheel over the circumference thereof substantially in the shape of a spiral, and therefore the channel is for example a turbine spiral or a spiral segment.
The half-axial turbine is a compromise between the simple radial turbine and the simple axial turbine. Furthermore, the half-axial turbine is suitable for being adapted, in particular when the blades of the turbine wheel are strictly radial, to desired tip-speed ratio ranges without mechanical reductions having to be accepted, meaning that advantages with respect to the degree of effectiveness can be achieved compared with simple radial turbines and simple axial turbines. The tongue slide is in this case a simple turbine variability which can be implemented in a manner that is favorable in terms of installation space and cost and exhibits a high degree of thermal robustness.
It has proven to be particularly advantageous for the tongue to have at least one trailing edge by means of which the exhaust gas flows off the tongue toward the receiving region when the turbine is operated. The trailing edge extends at least in part along a theoretical surface that extends conically in the axial direction of the turbine wheel.
In a further embodiment of the invention, the turbine wheel has rotor blades having respective leading edges by means of which the exhaust gas flows against the turbine wheel when the turbine is operated, the respective leading edges extending at least in part along a theoretical surface that extends conically in the axial direction of the turbine wheel. This extension of the trailing edge or leading edge allows a particularly efficient operation. Therefore, whereas for example tongue trailing edges of the turbine housing and the trailing edge of the tongue in the case of simple radial turbines predominately lie on a cylindrical surface, the trailing edges of the tongue and also the leading edges of the rotor blades in the case of the half-axial turbine are at least predominately oriented on conical surfaces, and, in the meridian view, have an angle with respect to the axis of rotation that differs significantly from 0 and is in a range of from 20° inclusive to 60° inclusive.
The use of a half-axial turbine allows a degree of freedom with respect to the design of the blade inlet angle compared with the simple radial turbine. The blade inlet angle is in particular understood to mean the angle at which the exhaust gas flows against the particular rotor blade of the turbine wheel when the turbine is operated. In the case of the simple radial turbine, a blade inlet angle of at least substantially 90° with respect to the circumferential direction is usually required on grounds of stability. With respect to the combination of the half-axial turbine, or turbine wheel of the half-axial turbine, with the variability, which acts as an inlet variability and is designed as a tongue slide, there are a wide range of favorable possibilities for adapting the optimum degree of effectiveness to the tip-speed ratio range of from approximately 0.5 up to the value of 0.8 for a very advantageous operation of the internal combustion engine.
In a further embodiment of the invention, the tongue is arranged in the axial direction of the turbine between cover rings of the tongue slide, is connected to the cover rings and is rotatably mounted on the turbine housing by means of the cover rings. The cover rings form for example respective, at least substantially cylindrical running surfaces, which the cover rings are for example at least indirectly rotatably mounted on the turbine housing.
A further embodiment is characterized in that at least one of the cover rings is sealed off from the turbine housing by means of at least one sealing element. Preferably, both rings are sealed off from the turbine housing by means of respective sealing elements. The relevant sealing element is arranged for example on the above-mentioned, at least substantially cylindrical running surface. By sealing the relevant sealing ring off from the turbine housing, leakage and flow losses can be kept particularly low, and therefore a particularly efficient operation of the turbine can be shown.
It has also proven to be particularly advantageous for the tongue to be coupled to an actuator by one of the respective cover rings, by means of which actuator the tongue is rotatable or slidable relative to the turbine housing about the axis of rotation. As a result, the installation space requirements, the number of parts and the weight of the turbine can be kept particularly low, and therefore a particularly efficient and thus energy-saving operation can be shown.
In order to realize a particularly efficient operation, in a further embodiment, at least one contour piece is provided that is separate from the turbine housing and separate from the tongue slide and is held at least indirectly on the turbine housing, and by means of which at least part of the turbine wheel is covered outwardly in the radial direction, and in the axial direction. Since the contour piece is separate from the turbine housing, separate from the turbine wheel and separate from the tongue slide, a gap can be set as needed between the contour piece and the turbine wheel by means of the contour piece. On account of the precise and needs-based setting of the gap, the gap can be kept particularly small, and therefore flow and leakage losses can be kept particularly low.
In this case, it has proven to be particularly advantageous for one of the cover rings to be at least partly covered by the contour piece inwardly in the direction of the turbine wheel. As a result, undesired flows and thus flow losses can be kept particularly low, and therefore a particularly efficient operation can be shown.
A further embodiment is characterized in that the tongue slide is rotatably mounted on the contour piece by means of one of the cover rings. As a result, a particularly advantageous and therefore efficient operation of the turbine can be realized.
Further advantages, features and details of the invention can be found in the following description of a preferred embodiment and with reference to the drawings. The features and combinations of features stated above in the description as well as the features and combinations of features stated below in the description of the figures and/or shown in the figures alone can be used not only in the combination specified in each case, but also in other combinations or in isolation without departing from the scope of the invention.